Not responding when people are expecting or hoping for a reply is ignoring. If I walk up to you on the street and say "hello" and though you heard me, you do not respond, you are ignoring me. If I send you an email and you read it and don't respond, you are ignoring me. If people post suggestions and you do not respond, you are ignoring them.
How tough is it to respond? I bet 99% of the discussions here could be ended with one of four simple one-sentence replies:
1. "This suggestion has already been rejected." (leave it to them to discuss why, or to find the original thread)
2. "This is a good suggestion, but cannot be implemented soon due to the coding/technology required."
3. "This suggestion has been considered, but is a lower priority than some other changes we are currently working on."
4. "This is a good idea and will be picked up and implemented quite fast."
Like most managers, I enjoy this game and the SP community, and thank you very much for creating it. But I also want it to change and grow and improve. And I fail to see how this change is an improvement, or how the SP managers should be encouraged that they are being heard. At best, it's an acknowledgment that their proposals were largely disregarded before, and they can expect the same in the future. If you still encourage people to suggest improvements, why would you close down the forum dedicated to such requests? If you didn't respond enough before, how will you be more responsive now? You won't. And that is disappointing.
Hard to answer this one, because you are right in some things you say.
I've decided quite some time ago to no longer answer the topics in which I didn't have anything useful to say. Just answering each post with one of your 4 options, would take me too much time. I know it seems like it would not take much time, but 10 minutes a day on average adds up to an hour each week. That's really hard to keep up for years and years ... Especially if there are so many similar things to do which also take up time (handle all incoming mails, handle advertising, handle the difficult sheriff cases, handle moderator disagreements, handle translations and translators, fixing bugs, ...). It's only after all of things have been done, I can start working on new features.
Therefor I feel it's unfair to encourage managers to come up with ideas. Nevertheless I do think it's important to say, that if a manager still has an idea he wants to share, he is welcome to post it in the other forum section.